Conventionally, electronic parts such as resistors, for example, are manufactured by electroless nickel plating. In this method, ceramic chips are immersed in a plating solution containing nickel sulfide (NiSO4.7H2O), hypophosphorous soda (or sodium hypophosphite NaH2PO2), a chelating agent and a stabilizer. The solution temperature is maintained at 80.degree. to 93.degree. C. Then each ceramic chip is coated with a plating layer of a ternary or multiplex alloy of nickel (Ni), chromium (Cr), phosphorus (P) and other metals.
The above known method, since the pH value of the plating solution changes with passage of time during the electroless plating reaction, provides a very poor yield in the manufacture of resistors having an initial resistance of 0.02 to 100 ohm or more and a temperature coefficient of resistance (TCR) of a two-digit figure or less in ppm. The plating operation must be followed by a troublesome operation of sorting the resistors into those having a temperature coefficient of resistance (TCR) of a three-digit figure in ppm and low-range resistors having a temperature coefficient of resistance (TCR) of a two-digit figure in ppm, the latter being produced accidentally. With the known method, it has been difficult to obtain electronic parts such as low-range resistors having uniform electric characteristics.
Most of the electronic parts obtained by the above known method have a temperature coefficient of resistance of high, three-digit ppm value, and therefore extensive resistance variations occur with temperature variations. Such electronic pars are hardly suited for use in outside atmosphere, for example, where temperature variations take place to a great extent.